To date, astronomers have catalogued over 860 exoplanets. If that wasn't remarkable enough, scientists have also been able to determine the atmospheric composition of many of these planets by analyzing their spectral shifts. But even more incredible would be the ability to actually chart landmasses and oceanic expanses. According to scientist Nicolas Cowan, this might actually be possible — and he says he knows how to do it.

Top image: An EPOXI mission image shows what an Earth-like exoplanet might look like from a great distance (NASA/JPL-Caltech/UMD/GSFC).

Cowan, who works at Northwestern University in Evanston, Illinois, presented his plan at this month's meeting of the American Astronomical Society in Long Beach, California. His idea is that software will eventually be able to take reflected starlight and tease it apart to form rudimentary maps of exoplanetary surfaces. It's a technique that was inspired by a pre-existing technology that's currently being used to distinguish natural from unnatural surfaces on Earth.

As Ker Than of LiveSciencereports, Cowan tested his software program on images of Earth taken by NASA's Deep Impact spacecraft from a distant vantage point in space. He was able to parse out critical features, including land, ocean, and clouds.

The technique, called "rotational unmixing," analyzes the changing color of starlight reflecting off a distant exoplanet as it spins. The software calculates the mix of planetary features that generate a specific hue. It's akin to watching a TV image reflected off a surface; it's far from perfect, but a basic image emerges.

Than writes:

Lisa Kaltenegger, an exoplanet researcher at the Max-Planck Institute for Astronomy in Heidelberg, Germany, said Cowan's technique was very interesting– but with a few caveats. For example, the exoplanet must have highly contrasting surfaces, such as ocean and land, or ocean and clouds, for this technique to work well.

"If you have an ocean planet or a planet that is all land, it would be very challenging because you don't have different surfaces," said Kaltenegger, who also did not participate in the study.

Another challenge would be distinguishing between clouds and ice on a planet's surface, according to Aomawa Shields, an astrobiologist at the University of Washington in Seattle who was not involved in the study.

"Being able to tell whether a planet is simply undergoing significant cloud cover, or is in the midst of a global glaciation is important from the standpoint of habitability," Shields said.

In terms of when this technique can be used to study the surfaces of distant planets, Cowan said it will require "a next-gen" telescope, something that may become available in the early 2020s.